A fluid-air exchange procedure involves the infusion of air into the eye as fluid is aspirated out of the eye. An air-gas exchange, to follow, injects a volume of gas mixed with air into the eye displacing and replacing the air originally in the eye. Obtaining a desired mixture of gas and air along with ensuring that the resulting mixture delivered to the posterior segment of the eye is correct leads to excessive waste of gas and surgical time. Consequently, large volumes of these gases beyond what are needed to occupy the posterior segment are released into the environment and surgery is delayed during the gas and air mixing process.